Multi-screw extruder

ABSTRACT

The invention relates to a multi-shaft extruder for the continuous treatment and/or processing of bulk material, especially a powdery, granular or flocculent product, comprising a plurality of shafts ( 3 ) which are arranged in a crown-like manner in a cavity ( 1 ) of an extruder housing ( 2 ), said shafts extending parallel to the axial direction (A) of the extruder and forming an inner processing chamber ( 1   a ) inside the crown, and an outer processing chamber ( 1   b ) outside the crown. Each shaft carries a number of axially successive processing elements ( 4 ), at least part of the same being elements ( 4   a   ; 4   c   ; 4   e ) having a transporting effect, and with which adjacent shafts engage in a sealed manner at least in partial regions. At least one transporting endless screw element ( 4   b   ; 4   d   ; 4   f ) comprising at least one transporting screw thread ( 9, 10; 14, 15, 16; 19, 20 ) is placed in the region of the supply opening ( 21 ) in the extruder housing ( 2 ), and does not engage in a sealing manner in at least one partial region along the axial direction (A).

BACKGROUND OF THE INVENTION

The invention relates to a multi-screw extruder for the continuousprocessing and/or working of a bulk material, in particular a powder,grain or flaked product, and to a method for filling the processingspaces of such a multi-screw extruder.

Multi-screw extruders for processing and/or working bulk material areknown in the art. A special group of multi-screw extruders has parallelabutting screws divided into a first process space and second processspace for processing the product inside the extruders. In areas wherethe processing elements are tightly meshing conveying elements, there isessentially no connection to enable an exchange of material between thefirst process space and the second process space at least in this area.At most gases and traces of the most finely distributed product can getfrom one to the other process space. The impossibility of any productexchange between the two process spaces is particularly disadvantages inthe feed zone of such a multi-screw extruder with several process spacesif only one of the process spaces can be filled with product via thefeed hole of the extruder. The other process space(s) in this feed zoneis/are filled with extremely small quantities of the product, if any.This translates into a waste of process space volume and a limitation ofproduct feed capacity of the extruder. This is particularlydisadvantageous in the case of a ring extruder with several screwsarranged as a rim in a hollow space of its casing, which run parallel tothe axial direction of the casing and form an inner process space insidethe rim along with an outer process space outside the rim. Only theouter process space outside the rim is here filled with product via thefeed hole, while the inner process space remains unused in the area ofthe feed hole. In the end, this feed limitation allows only a fractionof the potential throughput to be realized with this ring extruder.

One potential solution to this is offered by DE-196 04 228, whichdiscloses such a ring extruder for the continuous processing offree-flowing materials. In this case, the aforementioned problem of feedlimitation is resolved by forming at least one opening in the screw rimby omitting the conveying properties of at least one processing elementin the area of the material feed hole in the process space of the ringextruder. Instead of a conveying screw element, a spacer sleeve with asmooth outer cylinder wall is used in this area on the mandrel of atleast one of the screws of the rim in the area of the material feedhole. While this enables a material exchange between the outer and innerprocess space in the area of the feed hole, it does so at the cost ofthe conveying properties in this area. As a result, a portion of theproduct passed through the material feed hole remains in the dead spacesof the feed zone, so that optimum use is still not made of the volume ofthe inner process space.

SUMMARY OF THE INVENTION

The object of the invention is to solve the problems of prior artmentioned at the outset, and in particular to overcome the feedlimitation for a ring extruder of the design mentioned above.

This object is achieved with a device according to the characterizingfeatures of claim 1, and with a method according to the features ofclaims 19 and 20.

The underlying idea of this solution according to the invention is to atleast partially remove a web in at least double-threaded elements. Thisis because the continuous self-cleaning and tight meshing of theErdmenger profiles can be omitted in the feed zone. However, thisenables a product exchange between the inner process space and the outerprocess space of the ring extruder mentioned at the outset. As a result,the entire volume of both the inner and outer process space of theextruder can be utilized over its entire processing length. In addition,the conveying effect of the only partially removed conveying elementsstill present in the entire feed zone makes it possible to prevent deadvolumes in the feed zone. The product is hence uniformly distributed inboth process spaces from the very start, i.e., the same product quantityper volume is fed to the inner and outer process space and continuouslyremoved from this area. This eliminates the need to use non-tightlymeshing elements away from the conveying area of the feed zone tobalance out the product quantity in the inner and outer process space.

The significant advantage according to the invention that there is nodead space in the fill zone means that the product finds no space inwhich it can become deposited. This 100% removal of the product from thefill zone ensures that the entire available volume can be used toaccommodate newly added product. There is no impediment by residualproduct, and no unnecessary retention time of the product as the resultof downstream “compensation elements”. The later are hence omittedentirely, which decreases the investment costs for such an extruder, andreduces the overall retention time of the product in such a process.Eliminating such “compensation zones” for the method according to theinvention, which are completely contained in the modified fill zonebased on the invention, makes it possible to use the process space ofthe extruder for other purposes, or omit it entirely, which yields anoverall shorter processing zone, and hence reduces investment and spacerequirements for the extruder according to the invention. Anotherpotential disadvantage of such “compensation zones” of prior art is thatthey lie in an area of the method used for other processing purposes,e.g., the melting zone. Omitting these “compensation zones” in this casemakes it sufficient to use only tightly meshing elements for melting,for example, which results in a shorter overall retention time of theproduct in the extruder and, in the case of PET, in less damage to theproduct.

It makes sense to only use conveying screw elements in the area of thefeed hole, wherein in particular the at least one conveying screwelement has a gap toward the adjacent screw element alongside the screwelements whose projected surface lying in the plane in which run the twolongitudinal axes or rotational axes of the screws arranged on eitherside of the gap, a radial dimension ΔR and a dimension ΔL alongside thescrew elements.

This gap formed by the at least one conveying screw element toward theadjacent screw element is preferably dimensioned in such a way that itsradial dimension ΔR ranges between about 1/30 and ½ of the screw shankouter diameter Da, and in particular between 1/10 and ¼ of the screwshank outer diameter, wherein the axial dimension ΔL of the gapalongside the screw elements is derived from dimension ΔR and the pitchof the screw elements, and in particular measures about 2ΔR. Thisenables both a sufficiently conveying effect along the product conveyingdirection and a sufficient exchanging effect between the outer and innerprocess space of the extruder.

The pitch of the webs of the screw elements in the feed zone bestmeasures at least 0.5 times, preferably at least 1 times the outerdiameter Da of the screw elements. This permits a swift removal of thesupplied product from the area of the feed hole. This is particularlyadvantageous for preparing recycled PET (RPET) in such a ring extruder.

The ratio between the outer diameter Da and inner diameter Di of thescrew element best lies between 1.4 and 1.9.

The leading edge of the conveying screw elements preferably runsperpendicular to the axial direction of the extruder, at least at theradial edge area of the webs of the screw elements. This facilitates theconveying effect of the screw elements.

The trailing edge of the conveying screw elements also preferably runsperpendicular to the axial direction of the extruder, at least at theradial edge area of the webs. This also helps increase the holdingcapacity of the ring extruder according to the invention for loose bulkmaterial like RPET flakes or RPET chips.

Other advantageous embodiments of the leading edge at the radial edgearea of a web of conveying elements are characterized in that theleading edges run in the conveying direction overlapping theperpendicular to the axial direction, or that the leading edges areconcave at least at the edge area of the webs. As an alternative or inaddition, the leading edges (active edges) can also be back cut at theedge area of the webs. All of these measures also help improve theconveying capacity of screw elements designed in this way.

In a particularly advantageous embodiment of the invention, the axialpartial area of the hollow space containing the screws located in thearea of the feed hole is radially expanded, and this radial expansionextends along a portion of the screw rim in its circumferentialdirection. This step increases the process space volume in this axialpartial area at the feed hole, which is particularly advantageous forthe feed behavior of the extruder according to the invention for loosebulk material. In particular when preparing RPET, which is compacted andlater melted when processed, this has a particularly advantageouseffect.

The expansion here preferably extends along the circumference of thescrew rim in the circumferential direction on either side away from thefeed hole, and extends between the respective radially outer surface ofthe hollow space and the screw rim. This enables a particularlyeffective feeding of the ring extruder both in its outer process spacevia expansion along the circumference of the screw rim, as well as inits inner process space through the gap or gaps. A stuffing screw can beattached to the feed hole to increase the feed capacity. In addition,the extruder casing can still have vent holes in proximity to the feedhole, which are preferably exposed to a pressure below atmosphericpressure. This makes it possible to increase the feed capacity for loosebulk material even further for the extruder according to the invention.

In another preferred embodiment, at least one web is removed in theextruder according to the invention with at least one multi-threadedconveying element in the fill zone. One of the webs can be completelyremoved in a two-web conveying element, or even two of the three webs ina triple-threaded conveying element can be removed. It is sufficient forone of the webs to be present throughout for each conveying element, andinteract with its adjacent conveying element in a tightly meshing andmutually stripping manner. The free space obtained by omitting the websalso has a positive effect on the feed behavior of the ring extruderaccording to the invention.

In the method according to the invention in claim 19, the multi-screwextruder according to the invention described at the outset can befilled with the bulk material to be processed and/or worked, inparticular a powder, grain or flaked product, wherein the product issupplied on the outside of the screw rim and distributed in the area ofthe feed hole on the inner process space and the outer process space ofthe multi-screw extruder. In other words, a portion of the suppliedproduct stream is drawn into the inner process space and axiallyconveyed by the at least one screw element that is not tightly meshingalong the axial direction in at least one partial area. A portion of theproduct stream is here drawn into the inner process space through the atleast one gap that forms between the at least one conveying screwelement and an adjacent screw element. The entire inner process space ishere constantly evacuated by the partially removed but yet continuallyconveying screw elements in the area of the feed hole. The product canbe drawn to the outside of the screw rim by gravitational force and/orwith a stuffing screw. The feed capacity can be further increased bykeeping the process space of the ring extruder at a pressure belowatmospheric pressure in the area of the feed hole.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description of preferred embodiments of the inventionlists additional advantages, features and potential applications of theinvention.

FIG. 1 shows a section through a ring extruder according to theinvention along line 1—1 of FIG. 2 perpendicular to axial direction Athrough the extruder.

FIG. 2 shows a diagrammatic top view of the ring extruder according tothe invention from FIG. 1.

FIG. 3A shows a view of the screw elements in the feed zone of amulti-screw extruder according to a first exemplary embodiment in asection perpendicular to axial direction A.

FIG. 3B shows the feed zone of FIG. 3A viewed form the direction ofarrow P.

FIG. 4A shows a view of the screw elements in the feed zone of amulti-screw extruder according to a second exemplary embodiment in asection perpendicular to axial direction A.

FIG. 4B shows the feed zone of FIG. 4A viewed from the direction ofarrow P.

FIG. 5A shows a view of the screw elements of the feed zone of amulti-screw extruder according to a third exemplary embodiment in asection perpendicular to axial direction A.

FIG. 5B shows the feed zone of FIG. 5A viewed from the direction ofarrow P.

FIG. 6 shows a section through the feed zone of a ring extruderaccording to a fourth exemplary embodiment perpendicular to axialdirection A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a partial section through a 12-screw ring extruderperpendicular to axial direction A along a sectional plane 1—1 (see FIG.2). This sectional view describes both the section through a ringextruder according to prior art as well as through a ring extruderaccording to this invention. The extruder casing 2 consists of a core 2a and outer casing 2 b. Extending between the core 2 a and outer casing2 b is a rim-like hollow space 1, which is divided into an inner processspace 1 a and an outer process space 1 b by screws 3 arranged in a rimin this hollow space 1, which each carry a processing element orconveying element 4. The processing elements 4 shown here aredouble-threaded conveying elements each with a first flight 41 and asecond flight 42. The screw profile (along axial direction A) ispreferably designed in such a way that adjacent conveying elements 4always contact each other, so that the first web 41 and second web 42 ofa conveying element 4 is in contact with the core 43 or 44 of arespective adjacent conveying element 4. This profile (Erdmengerprofile) ensures that all conveying elements 4 always strip each other.At the same time, this also separates the inner process space 1 a fromthe outer process space 1 b at least in this axial area of the ringextruder, not allowing an exchange of product between the two processspaces. Only very small quantities of product and gas can be exchangedbetween the inner process space 1 a and the outer process space 1 b. Acontinuous self-cleaning also takes place between the concave innercylinder segments 5 a of the radially inner surface 5 of the hollowspace 1 and the webs 41, 42 of the conveying elements 4. In the sameway, the concave outer cylinder segments 6 a of the radially outersurface 6 are always contacted by the webs 41, 42 of the conveyingelements 4 and freed of any adhering product. The processing elements(e.g., conveying elements) 4 are each secured to their respective screw3 by a positive, fixed connection.

FIG. 2 is a diagrammatic top view of a ring extruder according to theinvention shown on FIG. 1. Discernible through a feed hole 21 in theextruder casing 2 is the screw rim with its processingelements/conveying elements 4. A total of six screws, i.e., the upperhalf of the screw rim, are visible. A radial expansion 22 of the outerprocess space 1 b is provided between the radially outer surface 6 ofthe outer process space 1 b and the outer surface of the screw rimformed by the processing elements 4. In addition, the two uppermostprocessing elements 4 are “removed” in such a way as to generate a slitS between them, through which the outer process space 1 b with the innerprocess space 1 a (see FIG. 1) is connected. Of course, correspondingslits can also be provided between the other adjacent processingelements/conveying elements 4 instead of the one shown slit S. Whencombined, this slit or these slits and the radial expansion 22 of theouter process space generate a considerable increase in the feedcapacity of the ring extruder according to the invention for bulkmaterial. The increase in feed capacity is particularly pronounced forloose bulk material, e.g., recycled RPET present in the form of chips orflakes.

FIGS. 3A and 3B show the screw elements in the feed zone of amulti-screw extruder according to the invention. For the sake ofsimplicity, the screws with the conveying elements 4 a and 4 b are notshown in their rim-like configuration, but rather shown in a flatarrangement that borders the outer process space 1 b open to the outside(see FIG. 1 and FIG. 2) relative to the inner process space 1 a. FIG. 3Ashows the feed zone in a section perpendicular to the axial direction Aalong section plane 3A—3A of FIG. 3B. FIG. 3B shows the feed zone ofFIG. 3A from the viewing direction denoted on FIG. 3A.

The conveying elements shown on FIGS. 3A and 3B are each double-threadedconveying elements 4 a, 4 b, 4 a, 4 b, wherein the conveying elements 4a each have two complete, unremoved webs 7 and 8, while the conveyingelements 4 b each have a partially removed web 9 and a completelyunremoved web 10. The partially removed web 9 of the conveying elements4 b is partially removed, so that a gap S is formed between theunremoved conveying elements 4 a and the partially removed conveyingelements 4 b in the areas 91, 92, 93, 94 and 95 in which the removed web9 lies opposite the core of the respectively adjacent conveying element4 a. The slit S has a radial dimension ΔR and axial dimension ΔL. If theconveying elements 4 a and 4 b rotate during operation, the slits Sformed between the adjacent conveying elements 4 a and 4 b move to andfro in axial direction A. In the case shown on FIGS. 3A and 3B, theratio of screw outer diameter Da to screw inner diameter Di measuresabout 1.3.

FIGS. 5A and 5B show a portion of the introduction zone of a multi-screwextruder according to the invention based on a third exemplaryembodiment of this invention. As opposed to FIGS. 3A and 3B as well as4A and 4B, only two conveying elements 4 e and 4 f from the feed zoneare shown. As on FIGS. 3A and 3B as well as FIGS. 4A and 4B, FIG. 5Ashows the two conveying elements 4 e and 4 f in a section plane 5A—5A ofFIG. 5B perpendicular to axial direction A, while FIG. 5B shows the twoconveying elements 4 e and 4 f from the viewing direction shown by thearrow P on FIG. 5A. The two conveying elements 4 e and 4 f aredouble-threaded conveying elements each with flights 17 and 18 or 19 and20. The flight 19 of conveying element 4 f is removed in the partialareas 191, 192, 193, 194, 195, 196 and 197, so that gaps S with a radialexpansion ΔR and axial expansion ΔL are also formed here in the removedareas between the conveying element 4 e with unremoved webs 17, 18 andthe conveying element 4 f with the removed web 19. The Da/Di ratio inthis case measures about 2.7. In the present exemplary embodiment, thegaps S have a particularly high radial expansion ΔR, which hisparticularly well suited for feeding RPET chips. While this diminishesthe strength (maximum transferable torque), it does yield lots of spacefor transporting RPET chips between the conveying elements. In the caseof a ring extruder, the power transmission from the drive will in thiscase be designed in such a way that the torque transmission is relayedby these “small-grained” (Da/Di large) feed elements and parallel tothese “small-core” feed elements via the “large-core” conveying elementsarranged primarily on the bottom of the rim, so that the “small-grained”conveying elements/feed elements.

FIG. 6 shows the fill zone of a ring extruder according to the inventionin a side view perpendicular to axial direction A. This exemplaryembodiment involves a ring extruder with ten screws 3, on whichconveying elements 4′ with web capping and conveying elements 4 withoutweb capping area arranged in the shown fill zone. In addition, theextruder casing 2 is expanded in the feed zone shown. The overallexpansion 22 of the casing 2 consists of an expansion 22 b of the outerprocess space 1 b (see FIG. 1) and an expansion of 22 a of the innerprocess space 1 a (see FIG. 1). Both the inner expansion 22 a and theouter expansion 22 b of the extruder casing 2 come about as the resultof having removed a portion of the material from both the radially innersurface 5 and radially outer surface 6 of the extruder casing 2. Theinner “flower” (see FIG. 1) formed out of the inner concave cylindersegments 5 a was removed from the radially inner surface 5, while theouter “flower” (see FIG. 1) formed out of outer concave cylindersegments 6 a was removed from the radially outer surface 6. Only on theleft side of the radially outer surface 6 on FIG. 6 was a portion of theouter concave cylinder segment 6 a retained. A conveying element 4′, 4,4″ is allocated to each of these three concave outer cylinder segments 6a. A conveying element 4′ with web capping is allocated to the uppermostof the three outer concave cylinder segments 6 a, while a conveyingelement 4 without web capping is allocated to each of the two lowerouter concave cylinder segments 6 a. Gaps were formed between adjacentconveying elements 4′ with web capping and between conveying elements 4′with web capping and conveying elements 4 without web capping. Sincethese gaps S move to and fro along the axial direction (perpendicular tothe plane of projection) during operation, only the gaps S that fallinto the sectional plane in the instantaneous rotational setting of theconveying elements 4′ and 4 are shown on FIG. 6. Of course, the gapswould shift given a further rotation of all conveying elements 4′ and 4in the sectional view on FIG. 6, so that a gap S comes about at leastonce during a total rotation of the conveying elements 4′ and 4 whilecompletely rotating the conveying elements 4′ and 4′ between alladjacent conveying elements 4′ and between all adjacent conveyingelements 4′ and 4. The capping of conveying elements 4′ is dimensionedin such a way that the arising gaps S are large enough to allow RPETchips to easily get in the inner expanded process space 22 a. Inaddition, the radial expansion 22 a of the inner process space 1 a isformed along the entire periphery of the core 2 a, while the radialexpansion 22 b of the outer process space 1 b is expanded along a largeportion of the rim periphery along circumferential direction U. Only theaforementioned “remainder” of the outer flower formed by the three outerconcave cylinder segments 6 a of the radially outer surface 6 ensures aseal of the outer process space 1 b on the left side of the outer screwrim circumference on the drawing.

The exemplary embodiment of FIG. 6 is especially advantageous, since itachieves an increase in feed behavior relative to the ring extruderknown from prior art as the result of a four measures:

-   -   1. The gap S formed between the conveying elements in the area        of the feed hole 21 and in the area of the outer radial        expansion 22 b of the outer process space 1 b allow for an        easier transfer of product from the outer process space 1 b to        the inner process space 1 a.    -   2. The inner expansion 22 a constitutes an enlargement of the        inner process space 1 a due to the removal of the radially inner        surface 5 (removal of inner flower, see FIG. 1).    -   3. The outer expansion 22 b constitutes an enlargement of the        outer process space 1 b (by removing the outer flower, see FIG.        1).    -   4. The fact that all conveying elements 4 and 4′ in the feed        zone continue to convey despite the partial removal of screw        elements, the product accommodated in these expanded process        spaces 1 a, 22 a and 1 b, 22 b is always conveyed away        immediately, thereby achieving a significant increase in feed        capacity. The feed zone expanded according to the invention on        FIG. 6 increasingly narrows along axial direction A (see FIG.        2), so that the initially loose, incoming product is        increasingly compressed as it is fed through the gap S and along        the circumferential direction U, and later along axial direction        A and, if necessary (in the case of RPET), melted. In this way,        the extruder according to the invention can be operated at an        efficient fill level (and hence a sufficient throughput) even        when loaded with initially very loose (e.g., chips) bulk        materials.

1. A multi-screw extruder for the continuous processing and/or working of a bulk material, in particular a powder, grain or flaked product, with several screws arranged as a rim in a hollow space of an extruder casing, which run parallel to the axial direction of the extruder and form an inner process space inside the rim along with an outer process space outside the rim, wherein the intersecting points formed by the axis lines of the respective screws with an imagined plane perpendicular to the axial direction lie on a rim line, and wherein each of the screws carries a plurality of axially consecutive processing elements, of which at least a portion are conveying elements, and with which adjacent screws tightly intermesh at least in partial areas, wherein the extruder casing is provided at the radially inner and radially outer surface of the hollow space with axially parallel concave circular segments that serve as a guide for the axially parallel screws with their processing elements on the inside or outside of the screw rim, and wherein the extruder has a feed hole at its first axial end leading to the hollow space as well as an outlet hole for the product to be processed at its second axial end, wherein at least one conveying screw element with at least one conveying screw web is used in the area of the feed hole in the extruder casing, which is not tightly meshing in at least one partial area along the axial direction; wherein at least one conveying screw element forms a gap toward the adjacent screw element whose radial dimension ΔR ranges between about 1/30 and ½ of the screw shank outer diameter Da, and has an axial dimension ΔL alongside the screw elements that is derived from dimension ΔR and the pitch of the screw elements and measures about 2ΔR.
 2. The multi-screw extruder according to claim 1, wherein only conveying screw elements are present in the area of the feed hole.
 3. The multi-screw extruder according to claim 1, wherein the pitch of the web of the screw element measures at least 0.5 times the outer diameter Da of the screw element.
 4. The multi-screw extruder according to claim 1, wherein the pitch of the web of the screw element measures at least 1.0 times the outer diameter Da of the screw element.
 5. The multi-screw extruder according to claim 1, wherein the ratio between the outer diameter Da and inner diameter Di of the screw element lies between 1.3 and 1.9.
 6. The multi-screw extruder according to claim 1, wherein the leading edges of the conveying screw element run perpendicular to the axial direction, at least at the radial edge area of its webs.
 7. The multi-screw extruder according to claim 1, wherein the trailing edges of the conveying screw element run perpendicular to the axial direction, at least at the radial edge area of its webs.
 8. The multi-screw extruder according to claim 1, wherein the leading edges run in the conveying direction overlapping the perpendicular to the axial direction at the radial edge area of the webs.
 9. The multi-screw extruder according to claim 1, wherein the leading edges are concave at least at the edge area of the webs.
 10. The multi-screw extruder according to claim 1, wherein the leading edges are back cut at the edge area of the webs.
 11. A method for filling a multi-screw extruder according to claim 1 with a bulk material to be processed and/or worked, in particular a powder, grain or flaked product, wherein the product is supplied on the outside of the screw rim and distributed in the area of the feed hole on the inner process space and the outer process space of the multi-screw extruder.
 12. The method according to claim 11, wherein the entire inner process space is constantly evacuated by conveying screw elements in the area of the feed hole.
 13. The method according to claim 11, wherein the product is drawn to the outside of the screw rim by gravitational force.
 14. The method for filling a multi-screw extruder according to claim 1 with a bulk material to be processed and/or worked, in particular a powder, grain or flaked product, wherein the product on the outsides of the screw rim is supplied to the outer process space, and through which the at least one conveying screw element that is non-tightly meshing in at least one partial area along the axial direction draws and axially conveys a portion of the product stream in the inner process space.
 15. The method according to claim 14, wherein a portion of the product stream is drawn into the inner process space through the at least one gap that forms between the at least one conveying screw element and an adjacent screw element.
 16. The method according to claim 1, wherein the process space is held to a pressure below atmospheric pressure in the area of the feed hole.
 17. A multi-screw extruder for the continuous processing and/or working of a bulk material, in particular a powder, grain or flaked product, with several screws arranged as a rim in a hollow space of an extruder casing, which run parallel to the axial direction of the extruder and form an inner process space inside the rim along with an outer process space outside the rim, wherein the intersecting points formed by the axis lines of the respective screws with an imagined plane perpendicular to the axial direction lie on a rim line, and wherein each of the screws carries a plurality of axially consecutive processing elements, of which at least a portion are conveying elements, and with which adjacent screws tightly intermesh at least in partial areas, wherein the extruder casing is provided at the radially inner and radially outer surface of the hollow space with axially parallel concave circular segments that serve as a guide for the axially parallel screws with their processing elements on the inside or outside of the screw rim, and wherein the extruder has a feed hole at its first axial end leading to the hollow space as well as an outlet hole for the product to be processed at its second axial end, wherein at least one conveying screw element with at least one conveying screw web is used in the area of the feed hole in the extruder casing, which is not tightly meshing in at least one partial area along the axial direction, wherein the axial partial area of the hollow space containing the screws located in the area of the feed hole is radially expanded, and the radial expansion extends along a portion of the screw rim in its circumferential direction.
 18. A multi-screw extruder for the continuous processing and/or working of a bulk material, in particular a powder, grain or flaked product, with several screws arranged as a rim in a hollow space of an extruder casing, which run parallel to the axial direction of the extruder and form an inner process space inside the rim along with an outer process space outside the rim, wherein the intersecting points formed by the axis lines of the respective screws with an imagined plane perpendicular to the axial direction lie on a rim line, and wherein each of the screws carries a plurality of axially consecutive processing elements, of which at least a portion are conveying elements, and with which adjacent screws tightly intermesh at least in partial areas, wherein the extruder casing is provided at the radially inner and radially outer surface of the hollow space with axially parallel concave circular segments that serve as a guide for the axially parallel screws with their processing elements on the inside or outside of the screw rim, and wherein the extruder has a feed hole at its first axial end leading to the hollow space as well as an outlet hole for the product to be processed at its second axial end, wherein at least one conveying screw element with at least one conveying screw web is used in the area of the feed hole in the extruder casing, which is not tightly meshing in at least one partial area along the axial direction; wherein an expansion extends along the circumference of the screw rim on either side away from the feed hole, and extends between the respective radially outer surface of the hollow space and the screw rim.
 19. A multi-screw extruder for the continuous processing and/or working of a bulk material, in particular a powder, grain or flaked product, with several screws arranged as a rim in a hollow space of an extruder casing, which run parallel to the axial direction of the extruder and form an inner process space inside the rim along with an outer process space outside the rim, wherein the intersecting points formed by the axis lines of the respective screws with an imagined plane perpendicular to the axial direction lie on a rim line, and wherein each of the screws carries a plurality of axially consecutive processing elements, of which at least a portion are conveying elements, and with which adjacent screws tightly intermesh at least in partial areas, wherein the extruder casing is provided at the radially inner and radially outer surface of the hollow space with axially parallel concave circular segments that serve as a guide for the axially parallel screws with their processing elements on the inside or outside of the screw rim, and wherein the extruder has a feed hole at its first axial end leading to the hollow space as well as an outlet hole for the product to be processed at its second axial end, wherein at least one conveying screw element with at least one conveying screw web is used in the area of the feed hole in the extruder casing, which is not tightly meshing in at least one partial area along the axial direction; wherein at least one web is removed in the fill zone for at least one multi-threaded conveying element. 